1. Field of the Invention
The present invention relates to a print method that rotates a disc-shaped recording medium, such as a CD-R (Compact Disc-Recordable) or a DVD-RW (Digital Versatile Disc-Rewritable), a semiconductor storage medium, or other printed object and prints visible information such as characters and designs by ejecting ink droplets onto a label surface or other print surface of the rotating printed object, and also relates to a print apparatus and recording medium driving apparatus that use such print method.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 09-265760 (JP 09-265760 A) discloses an example of a print apparatus that uses such print method. JP 09-265760 A relates to an optical disc apparatus that is capable of printing on a removable optical disc. The optical disc apparatus disclosed in JP 09-265760 A is an information storage apparatus that can carry out at least one of the recording and the reproduction of information using a removable optical disc. The apparatus includes: a print head that prints on the optical disc; a print head driving unit that moves the print head in the radial direction of the optical disc; a spindle motor that rotates the optical disc; and a control unit that controls the print head, the print head driving unit, and the spindle motor, wherein the control unit causes the print head to scan across the optical disc to print on the optical disc.
The optical disc apparatus disclosed in JP 09-265760 A constructed as described above has a stated effect of making it possible to print a label on an optical disc without having to separately provide a dedicated label printer and with the disc still inserted in the optical disc apparatus (see Paragraph [0059]).
However, the optical disc apparatus disclosed by JP 09-265760 A is constructed so as to print visible information on the label surface of an optical disc by ejecting ink droplets from ejection nozzles provided on a print head onto a rotating optical disc. Also, with an apparatus of this construction, there has been the problem that when printing is carried out with a constant rotational velocity for the optical disc and constant timing for the ejecting of ink droplets by the print head, the rotation of the optical disc causes displacements to occur in the impact positions of the ink droplets.
Japanese Unexamined Patent Application Publication No. 2004-330497 (JP 2004-330497 A) discloses an example of a print apparatus that can correct such displacements in the impact positions of the ink droplets. JP 2004-330497 A relates to a liquid ejecting apparatus. The liquid ejecting apparatus disclosed by JP 2004-330497 A includes a nozzle row where a plurality of nozzles for ejecting liquid to form dots on a medium are disposed in a row, and emits liquid from the nozzles to form a correction pattern on the medium, the correction pattern having a difference in darkness in the main scanning direction so that displacements in dot formation positions in the main scanning direction can be corrected based on the difference in darkness. In the apparatus, when liquid is emitted from the nozzles to form the correction pattern, at least two of the nozzles out of the plurality of nozzles that construct the nozzle row emit liquid at a different timing for each nozzle.
The liquid ejecting apparatus disclosed by JP 2004-330497 A with the construction described above has stated effects such as being able to form a correction pattern that makes it possible to accurately correct displacements in the dot formation positions in the main scanning direction (see paragraph [0092]).
The liquid ejecting apparatus disclosed by JP 2004-330497 A is constructed with an ejection head that scans in the main scanning direction and carries out printing on a print sheet that is conveyed in the subscanning direction, which is perpendicular to the main scanning direction, by ejecting ink droplets while making both a forward pass and a return pass in the main scanning direction. The correction pattern is formed before printing and displacements in the dot formation positions in the main scanning direction are corrected by matching up the timing at which ink droplets are ejected during the forward pass with the timing at which ink droplets are ejected during the return pass based on the correction pattern. In this way, the liquid ejecting apparatus disclosed by JP 2004-330497 A may not print on a rotating printed object and therefore may be not able to correct displacements in impact positions caused by ink droplets landing on a rotating printed object.
Next, displacements in impact positions due to ink droplets landing on a rotating printed object will be described with reference to FIGS. 1A and 1B. FIG. 1A shows a label surface 101a of an optical disc 101 such as a CD-R as a specific example of a printed object and a print head 102 from which ink droplets 103 are ejected. As shown in FIG. 1A, in the present example the print head 102 has eight ejection nozzles that are aligned in the radial direction of the optical disc 101. When the ink droplets 103 are ejected from the respective ejection nozzles, a total of eight ink droplets 103 land on the label surface 101a. FIG. 1B shows the case where printing has been carried out by ejecting the ink droplets 103 with a constant ejection timing using this type of print head 102 while rotating the optical disc 101 at a constant rotational velocity.
As shown in FIG. 1B, when printing is carried out with a constant rotational velocity for the optical disc 101 and constant timing for the ejecting of the ink droplets 103, the ink droplets 103 that are ejected in a line in the radial direction of the optical disc 101 will impact positions that are displaced in both the radial direction of the optical disc 101 and an angular direction measured relative to the origin for rotation angles. This displacement in the impact positions increases toward the outer periphery of the optical disc 101. This phenomenon occurs since the rotation of the optical disc 101 produces air flows in the periphery of the optical disc 101 and such air flows affect the ink droplets.
For example, if the radius of a dripped ink droplet 103 is expressed as a and the velocity of an air flow as v, the force F that acts on the ink droplet 103 due to such air flow is calculated byF=6πμva(Stokes drag)
where μ is the viscosity modulus of air.
The velocity v of an air flow produced in the periphery of the optical disc 101 increases toward the outer periphery of the optical disc 101. That is, the force F that acts due to an air flow is larger for an ink droplet 103 ejected at the outer periphery of the optical disc 101 than for an ink droplet 103 ejected at the inner periphery. Hence, different displacements occur in the impact positions of the ink droplets 103 according to the positions of such ink droplets 103 in the radial direction of the optical disc 101. As a result, distortion occurs in the printed visible information, which leads to a reduction in print quality.